A simple spectrophotometric determination of phorate using chromotropic acid

A new and simple spectrophotometric method for the determination of phorate, also known as "Thimet", a widely used systematic insecticide is proposed. The method is based on oxidation of phorate to sulphoxide and then to sulphones by coned, sulphuric acid and its hydrolysis in acidic conditions at similar to 100 degrees C to release formaldehyde which is then treated with chromotropic acid to produce a purple color dye, which has an absorbance maxima at 575 nm. Beer's law is obeyed in the range of 1-8 ppm of phorate. The method has been applied for the determination of phorate in river water, rice, wheat and cabbage samples. The method is free from the interference of most of the commonly used peticides.